Huygens’ Principle explains the diffraction of light by stating that every point on a wavefront acts as a source of secondary wavelets that spread out in all directions. When a wavefront encounters an obstacle or a narrow opening, not all parts of the wave can pass through directly. However, the points at the edge of the opening become new sources of wavelets.
These secondary wavelets then spread into the region beyond the obstacle, bending around the edges rather than continuing only in a straight line. This bending or spreading of light into the shadow region behind an obstacle is what we observe as diffraction.
The effect is more noticeable when the size of the opening or obstacle is comparable to the wavelength of light. In such cases, the overlapping secondary wavelets interfere with each other, creating patterns of bright and dark fringes. These patterns are the result of constructive and destructive interference between the diffracted wavelets.
Thus, Huygens’ Principle provides a visual and conceptual way to understand how light can bend around corners and produce diffraction patterns, supporting the wave nature of light.